WASHINGTON (AP) — The District of Columbia’s police chief says a police officer was shot in the chest but saved by his bulletproof vest while responding to the shootings at the Washington Navy Yard.

Chief Cathy Lanier says the officer “took two rounds” but survived the rampage last Monday that left 13 people dead, including the gunman. Another officer was shot in the legs and is still recovering in the hospital.

In an appearance Tuesday on NewsChannel 8′s “NewsTalk” program, Lanier called the response by police officers “heroic.”

The chief also said the design of the sprawling building where the shooting occurred was a “worst-case scenario” for police because it holds thousands of high-wall cubicles.

The FBI is still investigating what prompted 34-year-old Aaron Alexis, a former Navy reservist, to open fire with a shotgun.